In the field of medical technology, a large number of apparatuses are known with which fluids can be withdrawn from patients or fluids can be fed to patients via a hose line. The access to the patient generally takes place with a catheter for introduction into body organs or a cannula for the puncturing of vessels. During examination or treatment, a proper access to the patient must be ensured. It is therefore necessary to monitor the patient access.
A proper access to the patient is also required particularly for extracorporeal blood treatment apparatuses which comprise an extracorporeal blood circuit. The known extracorporeal blood treatment apparatuses include, for example, dialysis apparatuses or cell separators, which necessitate an access to the patient's vascular system. In extracorporeal blood treatment, blood is removed from the patient with an arterial puncture cannula via an arterial hose line, the blood being fed back again to the patient with a venous puncture cannula via a venous hose line.
Despite regular monitoring of the vascular access by hospital personnel, there is in principle the risk of the puncture cannula slipping out unnoticed from the patient's blood vessel. Whereas the slipping-out of the arterial cannula is associated with the sucking-in of air into the arterial hose line, the slipping-out of the venous cannula leads to the feared free flow of blood into the surroundings. If the slipping-out of the venous cannula is not therefore detected immediately, there is a risk of the patient bleeding to death. Even if the venous cannula has not slipped out completely, there is nonetheless the risk of relatively large quantities of blood issuing at the puncture point over the whole treatment period.
Various devices of differing design are known for monitoring the vascular access. The known monitoring devices generally rely on the safety devices present as standard in blood treatment apparatuses, said safety devices triggering immediate interruption of the extracorporeal blood treatment in the case of an incorrect vascular access.
Devices for monitoring a vascular access are known, which comprise a device for detecting moisture in order to be able to detect the issuing of blood at the puncture point.
The known devices for detecting moisture for use with the known monitoring devices for a patient access are constituted as a pad which is to be placed onto the wound or puncture point. The pad is made from an absorbent material in which a moisture sensor is embedded. A drawback is that false alarms are possible, for example due to perspiration on the skin or other bodily fluids, since it is not possible to distinguish with the moisture sensor whether the moisture at the wound or puncture point can be traced back to bleeding or for example to perspiration.
A device for monitoring a patient access, which comprises a device constituted as a pad for detecting moisture, is known for example from International PCT Application Publication WO 2006/008866 A1. The known device for detecting moisture is constituted as a mat, which is placed under the patient's arm which is punctured for the access to the vascular system. The mat is composed of a plurality of layers of different materials. Embedded between the upper and lower layers is the moisture sensor, which is made from a material layer which is printed with a meandering strip conductor, the ends whereof are designed as contacts. The moisture is detected by the fact that the resistance between the contacts of the strip conductor changes. The known device seeks to overcome the problem of false alarms due to perspiration by the fact that the layer with the strip conductor is covered by a hydrophobic filter with pores. The number and size of the pores should ensure that only larger, but not smaller quantities of moisture get to the moisture sensor.
U.S. Patent Application Publication No. 2005/0038325 A1 describes a device for detecting moisture for a device for monitoring a patient access, which is constituted as a pad which is placed on the puncture point. The pad again has a multi-layer structure, the moisture sensor again being embedded between the upper and lower layers. The known device for detecting moisture is characterized in that blood issuing at the puncture point enters into the lower layer at the underside of the pad lying on the patient's skin. The sensitivity is designed to be adjusted by the distance between the moisture sensor and the lower layer, in such a way that false alarms on account of perspiration are avoided.
The pad known from U.S. Patent Application Publication No. 2005/0038325 A1 comprises a section to which the cannula is fixed. The section is separated by a predetermined rupture line from the section in which the moisture sensor is disposed. The effect of this is that, in the event of an inadvertent tug on the hose line which leads to the cannula slipping out, only the section of the pad is torn off to which the cannula is fixed, but the section with the moisture sensor remains at the puncture point. This thus ensures that an alarm is triggered even in the case of an inadvertent tug on the hose line.
A device constituted as a pad for detecting moisture, wherein the blood enters at the underside of the pad, is also known from U.S. Pat. No. 6,445,304. With a sufficient thickness of the blood-permeable porous carrier material for the moisture sensor and with a suitable spacing of the strip conductors of the moisture sensor, it is intended to avoid a false alarm being triggered by only occasional seeping of blood or small quantities of other bodily fluids.
It is also known from U.S. Pat. No. 6,445,304 to provide in a pad to be placed on the puncture point a circular cutout, from which a slit extends up to the edge of the pad. This particular design of the pad makes it possible to put the pad in place even when the patient's vascular access is already punctured with a cannula. The slit makes it possible to displace the pad from the side over the cannula which is already in place and which then extends through the circular cutout. If the pad is placed on the patient's skin before the application of the cannula, the slit does however prove to be a drawback, since the slit pad loses stability.
The problem underlying the present invention is to provide a device easy to handle for detecting moisture for use with a device for monitoring an access to a patient, wherein the risk of the occurrence of false alarms, for example due to perspiration, is reduced. Moreover, the problem underlying the present invention is to provide a device for monitoring an access to a patient, in particular for monitoring the vascular access in an extracorporeal blood treatment, said device being easy to handle and permitting a reliable detection of the issuing of blood at the puncture point. It is also a problem underlying the present invention to specify an extracorporeal blood treatment apparatus with such a device for monitoring the vascular access.